ass日本风韵熟妇pics男人扒开女人屁屁桶到爽|扒开胸露出奶头亲吻视频|邻居少妇的诱惑|人人妻在线播放|日日摸夜夜摸狠狠摸婷婷|制服 丝袜 人妻|激情熟妇中文字幕|看黄色欧美特一级|日本av人妻系列|高潮对白av,丰满岳妇乱熟妇之荡,日本丰满熟妇乱又伦,日韩欧美一区二区三区在线

The unsteady numerical simulations were carried out to investigate the transient flow features of a centrifugal pump system at startup and valve-opening processes. The scale-adaptive simulation (SAS) based on SST turbulence model was used in the simulation. The computational domain was the entire closed double-suction centrifugal pump test rig. The transient head of the pump, the pressure pulsation on the casing and the radial force on the impeller were focused on. The results showed that the predicted transient head of the pump in startup processes agreed well with the experimental data. Compared with the steady-state calculations, the transient valve-opening simulation produced a pump head which was more close to the experimental data. The transient flow rate increased significantly with the increase of valve-opening time, while valve-opening speed almost did not affect the transient head. During the valve-opening process, the pressure pulsation on the volute changed cyclically, the dominant frequency equaled to the blade passing frequency. In addition, the most dramatic change in pressure pulsation amplitude was found in the region near the tongue. The radial force on the impeller decreased with the increase of the valve opening size, and it changed with the blade passing frequency.